Treating underground pollution of soil and water that is caused by leaked hydrocarbons or chemicals is a vexing problem. Underground tanks containing oils, benzene, gasoline and the like, have often leaked their contents slowly into the surrounding soils over decades. The pollutant has seeped slowly through and saturated different geologic strata that do not permit easy or quick flow. As a result, the removal of the pollution from such soils is difficult, time consuming and cost prohibited. A simple pumping out of ground water and treating it may temporarily lower the detected level of pollution, but over a period of time, additional contaminant leaches out of the contaminated soils and the level detected in the underground water goes back up. Leaching and water treatment out of the ground is described in U.S. Pat. No. 4,401,569. It has been suggested that the soil be, in effect, mined, removed, treated and then, perhaps, returned. See, for example, U.S. Pat. Nos. 5,415,777; 5,286,140; 5,172,709 and 4,849,360. These are expensive processes that involve a great deal of disturbance to the site and effectively remove the site from any economic use during the process.
It has also been suggested that fluids containing bioremediation agents be injected into the soil and water in situ. See for example, U.S. Pat. Nos. 5,133,625 and 5,304,704.
Although in situ bioremediation is becoming increasingly popular, the technical difficulties involved in delivering microbes, nutrients and oxygen to all the contaminated media have restricted its effectiveness. In the past, amendment fluids have been delivered through injection wells or infiltration trenches allowing natural migration to deliver the fluids throughout the contaminated media. While these techniques may be effective at high permeability sites, the results of in situ bioremediation at low permeability sites has typically been discouraging and ineffective.
Finally, combinations of these techniques with features such as steam injection and a multitude of wells (borrowed from oil field extraction) have been proposed. See for example, U.S. Pat. No. 5,279,740.
While these prior art techniques and systems have advantages in some circumstances, they all suffer from economic drawbacks or time drawbacks. That is, they are either quite expensive to carry out and disruptive of the site or they take a very long time to be effective especially when the pollutant is contaminated in difficult geologic soil conditions. There thus exists a need for an economical system that does not disrupt the site but which can deal with difficult and different underground soils in situ and still achieve substantial results in a reasonable period of time.